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I am new to electronics (using Arduino), begging to venture into creating my own circuits and not following set example. I would appreciate advice on the following.

When deciding upon how to power a circuit how exactly does one go about this? For example, I'm planning on using my Arduino Uno to control six MG996R servos via six potentiometers. For my understanding each:

  • MG996R servo requires: 5 - 6 V and 1.3 - 2.5 amps (stall to 6 V load working).
  • Arduino Uno: 5-7 V input and 40 mA per pin output // 5 V input being sufficient as I do not plan on using 5 V output.
  • Potentiometer: no specific / negligible volt/amp draw

Thus, to power the above I would require a power source of max 6 V (within operating limit of servo and sufficient for Arduino, and a total amp of:

  • 15A (6 x 2.5 amp for all six servos)
  • 240mA (6 x 6 pinouts on Arduino required to control PWM on servos). Total: 15.24 A

So overall for above I need a power supply: 6V, 15A. Is this correct?

If so, then my next question comes in how to power this from a battery? All the LiPo's (3S) I've used for drone etc thus far are 11.1V and 1500 - 3000 mA // way below the amps needed for above. Also I've always used a power distribution board to provide 5V to the Arduino, which provide only 2 - 3A.

I do have a external variable power supply but I'm reluctant to have 15A running as this seems considerably higher than anything I've used before and I don't trust my working. Also, I can't find a maximum amp limit for the Arduino, but feel that 15A would exceed its working limits.

I'm confused. Either I've got the workings completely wrong or I'm stuck at how to provide sufficient power to six servos using a battery, and not frying my Arduino at the same time.

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  • \$\begingroup\$ I think it would be reasonable to use a smaller number for the servo current. Unless you plan to stall all 6 servos at the same time, or think that is a fault condition that you want to handle without loss of power. Stall means that you command a position for the servo and it is unable to move to the commanded position, but just tries as hard as it can. I think a total of 6 or 7 Amps may be reasonable for your power supply or battery. This will probably allow you to stall one servo and not lose power. I am assuming that there are no major safety concerns here. Ultimately it is up to you. \$\endgroup\$
    – user57037
    Nov 15, 2020 at 21:48
  • \$\begingroup\$ Thanks. No safety issues, just a robotic arm I’m trying to make for fun. Amp wise, my calculation is based on max draw at 6V, so I understand that 15A would be the absolute max is all 6 servos were at max load - right? If so, then could easily get by with an Amp between the min (min being 500mA no load each servo do total 3A) 3-and 2A further per working servo. So say 7A would cover 4 servos ‘at rest’ and 2 at max load moving? Am I getting this? \$\endgroup\$ Nov 15, 2020 at 22:11
  • \$\begingroup\$ The main point is that stall is an abnormal condition. I would not provision for a power supply that can keep all 6 servos stalled indefinitely. It seems like 900 mA per servo may be more reasonable. Then add a little extra in case you stall one of the servos while you are experimenting. So 5 * 0.9 + 2.5 + arduino. \$\endgroup\$
    – user57037
    Nov 15, 2020 at 22:45
  • \$\begingroup\$ I am going by this datasheet which says that 500-900 is the operating current and 2.5A is the stall current. electronicoscaldas.com/datasheet/MG996R_Tower-Pro.pdf \$\endgroup\$
    – user57037
    Nov 15, 2020 at 22:49

1 Answer 1

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There is a battery eliminator circuit for your Arduino. BEC/UBEC etc. With this type of a circuit you can use your Arduino and motors together with the same power supply.

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  • \$\begingroup\$ 15 A is not that much for LiPo's? \$\endgroup\$ Nov 15, 2020 at 21:17
  • \$\begingroup\$ So are my calculations correct? 2.5A (max stall current) and 500mA (with no load) per servo means I’ll need 3A basic no load up to 15A with max load? Wow! \$\endgroup\$ Nov 15, 2020 at 21:19
  • \$\begingroup\$ Found some extra answers. I see that it’s not possible to provide ‘too much’ Amp as the arduino (or any component) will only draw what it needs. It’s only the volt I have to ensure is within safe operating limits - is that correct? If so then regarding BEC, this is only to drop voltage. So as arduino can tolerate up to 12v then I wouldn’t need a BEC in this case? \$\endgroup\$ Nov 15, 2020 at 21:58
  • \$\begingroup\$ @NicholasFarmer you are right. You can think that all the devices etc. you connected to the supply voltage as a load. These loads will draw current with respect to Ohm's law. Yes, if you dont need to change the voltage then BEC is unnecessary. \$\endgroup\$
    – ratatosk
    Nov 15, 2020 at 22:10
  • \$\begingroup\$ Thank you, really appreciate taking your time. I did search around a lot but needed an knowledgeable person to confirm. 👍 \$\endgroup\$ Nov 15, 2020 at 22:13

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